Wide field of view optical tracking system

ABSTRACT

In an optical tracking system for determining the pose of a moving object in a reference coordinate system, the system including at least one light emitter, at least one optical detector for detecting the light emitted by the at least one light emitter and a pose processor, coupled with the at least one optical detector, and with the at least one light emitter, for determining the pose of the moving object according to the light detected by the at least one optical detector.

This is the United States National Stage of Patent Cooperation TreatyApplication No. PCT/IL08/01252 filed Sep. 18, 2008, which claimspriority to U.S. Patent Application No. 60/975,325 filed Sep. 26, 2007.

FIELD OF THE DISCLOSED TECHNIQUE

The disclosed technique relates to tracking systems, in general, and toa Wide Field Of View (WFOV) optical tracking system for determining theposition and orientation of a moving object, in particular.

BACKGROUND OF THE DISCLOSED TECHNIQUE

Optical tracking systems for tracking the position and orientation of amoving object in a reference coordinate system are known in the art.These tracking devices employ optical detectors (e.g., Charge CoupledDevices) for gathering information about the position and/or orientationof a moving object. One configuration for such an optical trackingdevice is fixing one or several optical detectors on the moving objectand fixing a set of light sources (e.g., Light Emitting Diodes) at aknown position in the coordinate system. Another configuration for suchan optical tracking device is fixing a set of light sources on themoving object and fixing one or several optical detectors at a knownposition in the reference coordinate system. Yet another configurationis combining the former configurations and fixing both detectors andlight emitters on the moving object and at a known position in thereference coordinate system. Optical tracking systems enable automaticdecision making based of the determined position and/or orientation. Forexample, a pilot may aim at a target by moving only her head toward thetarget (i.e., the pilot does not have to move the aircraft toward thetarget). The optical tracking system determines the orientation (i.e.,elevation, azimuth and roll) of the helmet, worn by the pilot, in theaircraft coordinate system. As a further example, the optical trackingsystem may track the movements of a user of a virtual reality system(e.g., a game, a simulator) determining the position of the user.

However, an optical detector placed on the moving object can detect thelight emitters in the reference coordinate system only as long as thelight emitters are within the Field Of View (FOV) of the detector.Therefore, the FOV of the optical tracking system (i.e., the range ofpositions in which the optical tracking system tracks the moving object)is limited by the FOV of the optical detector. Similarly, the fixedlight detector can track the moving object as long as the light emittersattached to the moving object are within the FOV of the fixed lightdetector. Thus, the intersection of the FOV of the moving lightdetector, with the FOV of the fixed light detector, defines the trackingspace of the tracking system.

Reference is now made to FIG. 1, which is a schematic illustration of anoptical detector, generally referenced 10, which is known in the art.Optical detector 10 includes an optical sensor 12 optically coupled witha lens 14. Lens 14 includes an entrance pupil 16. The FOV φ of opticaldetector 10 is inversely proportional to the ratio between the focallength f of lens 14 and the size d of optical sensor 12. Furthermore,the accuracy of optical detector 10 is proportional to the angularresolution thereof. Therefore, when the size of sensor 12 (e.g., numberof pixels) is fixed, increasing the focal length of lens 14, increasesthe resolution but decreases the FOV of optical detector 10.

U.S. Pat. No. 3,678,283 issued to LaBaw, and entitled “RadiationSensitive Optical Tracker”, is directed to a system for determining thesight line of a pilot with respect to a point in a cockpit. The opticaltracker includes: two detector assemblies and three light emitters. Thefirst detector assembly is mounted on the helmet of the pilot. The firstlight emitter is mounted on the helmet of the pilot. The second detectorassembly is mounted on the cockpit, at the point. The second and thirdlight emitters are mounted on the cockpit, equally spaced on either sideof the bore sight line in front of the pilot.

The detector assemblies include lateral photo detectors able to detectthe lateral position of the light spot. The light emitters illuminate ata light frequency corresponding to the maximum sensitivity range of thedetectors. The two light emitters mounted on the cockpit illuminate thedetector mounted on the helmet. The illuminator mounted on the helmetilluminates the detector mounted on the cockpit. The determination ofthe azimuth and elevation angles, of the line of sight of the pilot, isirrespective of the helmet position within the cockpit. The amount ofroll of the head of the pilot is computed by the output of the helmetmounted detector, which detects the two cockpit mounted light emitters.

U.S. Pat. No. 5,767,524 issued to Barbier et al., and entitled “OpticalDevice for Determining the Orientation of a Solid Body”, is directed toa system for determining the orientation of a first solid body withrespect to a second, solid body. The orientation determination systemincludes: three sets of optical source/detector. Each opticalsource/detector set includes an optical source and an optical radiationdetector. At least one source/detector set is mounted on the first solidbody. At least one source/detector set is mounted on the second solidbody. On at least one of the solid bodies there are mounted twosource/detector sets.

The orientation system determines in the first referential system, ofthe first solid body, two straight lines corresponding to the lightradiation coming from the second referential system. The orientationsystem determines in the second referential system, of the second solidbody, two straight lines corresponding to the light radiation comingfrom the first referential system. The knowledge of the orientation ofat least two distinct straight lines in each of the referential systemsgives, by computation of the rotation matrix, the three parameters oforientation of the first solid body with respect to the referentialsystem of the second solid body.

SUMMARY OF THE PRESENT DISCLOSED TECHNIQUE

It is an object of the disclosed technique to provide a novel systemdetermining the position and orientation of a moving object in areference coordinate system.

In accordance with the disclosed technique, in an optical trackingsystem thus provided a Wide Field Of View (WFOV) optical detector, theWFOV optical detector. The optical tracking system tracks the pose of amoving object. The optical tracking system includes at least one lightemitter, at least one optical detector for detecting the light emittedby the at least one light emitter and a pose processor. The poseprocessor is coupled with the at least one optical detector, and withthe at least one light emitter. The pose processor determines the poseof the moving object according to the light detected by the at least oneoptical detector. One of the at least one optical detector and at leastone light emitter is situated at a fixed position in the referencecoordinate system, and the other of the at least one optical detectorand at least one light emitter is attached to the moving object. TheWFOV optical detector comprises an optical sensor and at least twooptical receptors optically coupled with the optical sensor. The opticalsensor senses light received from at least one of the at least one lightemitter. The optical receptors are spatially spaced apart from eachother. Each of the optical receptors projects a different angularsection of an observed scene on the optical sensor. The pose processorassociates at least one representation of the at least one light emitteron the optical sensor, with a respective one optical receptors whichprojects the light received from the at least one light emitter on saidoptical sensor, according the response of the optical sensor.

In accordance with another embodiment of the disclosed technique, thereis thus provided an optical tracking system for determining the pose ofa moving object in a reference coordinate system. The optical trackingsystem includes at least one light emitter, at least one WFOV opticaldetector and a pose processor. The WFOV optical detector includes anoptical sensor and at least two optical receptors optically coupled withthe optical sensor. The optical sensor senses light received from atleast one of the at least one light emitter. The optical receptors arespatially spaced apart from each other. Each of the optical receptorsprojects a different angular section of an observed scene on the opticalsensor. The pose processor is coupled with the at least one opticaldetector and with the at least one light emitter. The pose processorassociates at least one representation of the at least one light emitteron the optical sensor, with a respective one optical receptorsprojecting the light received from the at least one light emitter on theoptical sensor, according the response of the optical sensor. One of theat least one optical detector and at least one light emitter is situatedat a fixed position in the reference coordinate system, and the other ofthe at least one optical detector and at least one light emitter isattached to the moving object.

In accordance with a further embodiment of the disclosed technique,there is thus provided an optical tracking system for determining theorientation of a moving object in a reference coordinate system. Thesystem includes a moving optical detector, a reference optical detector,at least one moving light emitter, at least one reference light emitter,an orientation processor. The moving optical detector is attached to themoving object. The reference optical detector is situated at a fixedposition in the reference coordinate system. The at least one movinglight emitter is attached to the moving object and emits light from theentrance pupil of the moving optical detector. The reference lightemitter is situated at a fixed position in the reference coordinatesystem and emits light from the entrance pupil of said reference opticaldetector. The orientation processor is coupled with the moving lightemitter, the moving optical detector, the fixed light emitter and withthe fixed optical detector. The orientation processor determines anorientation angle of the moving object by subtracting a first angle froma second angle thereby determining the orientation angle of the movingobject in the reference coordinate system.

In accordance with another embodiment of the disclosed technique, thereis thus provided an optical tracking system for determining theorientation of a moving object in a reference coordinate system. Thesystem includes a reflective surface, a optical detector, at least onelight emitter and an orientation processor. The reflective surface isfixed in the reference coordinate system. The optical detector isattached to said moving object. The at least one light emitter isattached to said moving object. The optical detector detects lightreflected from said reflective surface. The orientation processor iscoupled with the optical detector and with the at least one lightemitter. The orientation processor determines the orientation of saidmoving object in said reference coordinate system according to the lightincident on said optical detector.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed technique will be understood and appreciated more fullyfrom the following detailed description taken in conjunction with thedrawings in which:

FIG. 1 is a schematic illustration of an optical detector, generallyreferenced 10, which is known in the art;

FIGS. 2A and 2B are schematic illustrations of a WFOV optical detectorassembly, generally referenced 100, constructed and operative inaccordance with an embodiment of the disclosed technique;

FIGS. 3A and 3B are schematic illustrations of WFOV optical detectorassembly, generally referenced 150, constructed and operative inaccordance with another embodiment of the disclosed technique;

FIG. 4 is a schematic illustration of an optical tracking system,generally referenced 200, for determining the pose (i.e., position andorientation) of a moving object 208 in a reference coordinate system inaccordance with a further embodiment of the disclosed technique;

FIGS. 5A, 5B, 5C and 5D are schematic illustrations of images of asingle light emitter acquired by a WFOV optical detector which includesonly two adjacent optical receptors;

FIG. 6 is an example for determining the horizontal orientation of amoving object without determining the position thereof in accordancewith another embodiment of the disclosed technique;

FIG. 7 is a schematic illustration of an optical tracking system,generally reference 250, constructed and operative in accordance with afurther embodiment of the disclosed technique; and

FIG. 8 is a schematic illustration of a two-dimensional example fordetermining the orientation of a moving object without determining theposition thereof in accordance with another embodiment of the disclosedtechnique.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The disclosed technique overcomes the disadvantages of the prior art byproviding an optical tracking system for determining the pose of amoving object including a moving optical detector and a referenceoptical detector. The term “pose” relates hereinafter to the position(i.e., the x, y and z coordinates) and the orientation (i.e., azimuthelevation and roll angles). According to one embodiment of the disclosedtechnique, the moving optical detector exhibits a novel configuration,for increasing the FOV thereof, without increasing the size of theoptical sensor or decreasing the focal length of the optical receptor(i.e., which decreases the accuracy of the tracking system). Accordingto another embodiment of the disclosed technique, the spatial setup ofthe light emitters and the detectors enables the optical tracking systemto determine the orientation of a moving object (e.g., a helmet), in areference coordinate system (e.g., the coordinate system of anaircraft), without determining the position of the moving object.According to a further embodiment of the disclosed technique, areflective surface replaces the reference detector, and also enables theoptical tracking system to determine the orientation of a moving object,in a reference coordinate system, without determining the position ofthe object.

As mentioned above an optical detector, placed on a moving object, candetect light emitters that are situated within the FOV of that opticaldetector. Therefore, increasing the FOV of the optical detectorincreases the tracking range of the tracking system. In order toincrease the FOV of the optical detector a plurality of opticalreceptors (e.g., lenses or pinholes or both) are placed over an opticalsensor. Additionally, the optical axes of the optical receptors may beunparallel with respect to each other. Thus, the field of view of thedetector is increased (i.e., relative to the FOV of a single opticalreceptor). Furthermore, the focal length of each optical receptor may bedifferent. It is noted that the WFOV optical detector according to thedisclosed technique, resolves objects in the WFOV thereof, when theangular span of these objects is substantially small (i.e., point likeobjects), such that the images of the object, formed on the opticalsensor by the various lenses, do not overlap with each other.

Reference is now made to FIGS. 2A and 2B, which are schematicillustrations of a WFOV optical detector assembly, generally referenced100, constructed and operative in accordance with an embodiment of thedisclosed technique. FIG. 2B is a side view of optical detector assembly100. Optical detector assembly 100 includes an optical sensor 102 andoptical receptors 104, 106, 108 and 110. Optical receptors 104, 106, 108and 110 are spaced apart from each other. Each one of optical receptors104, 106, 108 and 110 includes an entrance pupil. Optical receptor 104includes an entrance pupil 112, optical receptor 106 includes anentrance pupil 114, optical receptor 108 includes an entrance pupil 116and optical receptor 110 includes an entrance pupil 118. Opticalreceptors 104, 106, 108 and 110 may be optical lenses. Alternatively,Optical receptors 104, 106, 108 and 110 may be pinholes.

Optical receptors 104, 106, 108 and 110 are optically coupled withoptical sensor 102. Optical sensor 102 is, for example, a CCD detector,a Complementary Metal Oxide Semiconductor (CMOS) sensor, a PositionSensitive Device (PSD) or a lateral photo-detector. Optical receptors104, 106, 108 and 110 are arranged such that each element projectsdifferent angular sections of the observed scene (not shown) on the samearea of optical sensor 102. The FOV ν (FIG. 2B), of optical detectorassembly 100 is greater then FOV φ (FIG. 2B) of a single opticalreceptor such as optical receptor 106. Thus, the FOV of optical detectorassembly 100 is increased (i.e., relative to the FOV of a singleelement) without increasing the size d (FIG. 2B) of optical detector 100or decreasing the focal length f (FIG. 2B) of optical detector assembly100.

To increase the resolution at the center of the FOV of the opticaldetector, an additional optical receptor, with a larger focal length, isplaced above the optical receptors. Furthermore, to increase the FOV ofthe optical detector the bottom optical receptors are tilted, relativeto one another, such that the optical axes thereof are unparallel.

Optical detector 100 exhibits a unique response to the direction oflight incident thereupon. The position of the light incident on opticalsensor 102 is related to the direction from which light enters each ofentrance pupils 112, 114, 116 and 118. The unique response of theoptical detector to the direction of light incident thereupon isreferred to herein as the “directional response”. For example, when theoptical sensor 102 is a CCD sensor, each pixel in the CCD is associatedwith an angular step. When the optical sensor is a lateralphoto-detector, the current differences at the terminals of the detectorare related to the angle of light incident on the lateralphoto-detector.

Reference is now made to FIGS. 3A and 3B, which are schematicillustrations of WFOV optical detector assembly, generally referenced150, constructed and operative in accordance with another embodiment ofthe disclosed technique. FIG. 3B is a side view of optical detectorassembly 150. Optical detector assembly 150 includes an optical sensor152 and optical receptors 154, 156, 158, 160 and 162. Optical receptors154, 156, 158, 160 and 162 are spaced apart from each other. Each one ofoptical receptors 154, 156, 158, 160 and 162 includes an entrance pupiland a lens. Optical receptor 154 includes an entrance pupil 164, opticalreceptor 156 includes an entrance pupil 166, optical receptor 158includes an entrance pupil 168, optical receptor 160 includes anentrance pupil 170 and optical receptor 162 includes an entrance pupil172.

Optical receptors 154, 156, 158, 160 and 162 are optically coupled withoptical sensor 152. The FOV (FIG. 3B), of optical detector assembly 150is increased relative to the FOV of a single optical receptor (e.g.,optical receptor 106 in FIG. 2B) without changing the size d of opticalsensor 152 or the focal lengths of the lenses. As mentioned aboveoptical receptors 154, 156, 158, 160 and 162 may be optical lenses.Alternatively, optical receptors 154, 156, 158, 160 and 162 may bereplaced with pinholes. Optical detector 150 exhibits a directionalresponse.

Reference is now made to FIG. 4, which is a schematic illustration of anoptical tracking system, generally referenced 200, for determining thepose (i.e., position and orientation) of a moving object 208 in areference coordinate system in accordance with a further embodiment ofthe disclosed technique. System 200 includes a reference opticaldetector 206, reference light emitters 204 ₁ and 204 ₂, moving opticaldetector 210, a moving light emitter 212 and a pose processor 214.Either one of reference optical detector 206 or moving optical detector210 may be a WFOV optical detector as described hereinabove inconjunction with FIGS. 2A and 2B or FIGS. 3A and 3B. Pose processor 214is coupled with reference optical detector 206, with reference lightemitters 204 ₁ and 204 ₂, with moving optical detector 210 and movinglight emitter 212. Reference optical detector 206 and reference lightemitters 204 ₁ and 204 ₂ are situated at a known position 202 in areference coordinate system (not shown). Moving optical detector 210 andmoving light emitter 212 are attached to moving object 208. Moving lightemitter 212 and reference light emitters 204 ₁ and 204 ₂ are, forexample, Light Emitting Diodes (LEDs) emitting light at a desiredspectral range (e.g., visible light, infrared). Each of referenceoptical detector 206 and moving optical detector 210 exhibit adirectional response. Each of reference optical detector 206 and movingoptical detector 210 include an optical sensor (not shown). The opticalsensors are, for example, Charge Coupled Devices (CCDs), ComplementaryMetal Oxide Semiconductor (CMOS) sensor, a Position Sensitive Device(PSD) or a lateral photo-detector.

Reference optical detector 206 acquires an image of moving light emitter212. Moving optical detector 210 acquires an image of reference lightemitters 204 ₁ and 204 ₂. Pose processor 214 determines the pose ofmoving object 208 relative to the reference coordinate system accordingto the response of reference optical detector 206 and moving opticaldetector 210 to the acquired images of light emitters 204 ₁ and 204 ₂and moving light emitter 212.

It is noted that system 200 can determine the pose of moving object 208as long as reference light emitters 204 ₁ and 204 ₂ are within the FOV νof moving optical detector 210 and as long as moving light emitter 212is within the FOV of reference optical detector 206. It is further notedthat when moving optical detector 210 is a WFOV optical detector, eachoptical receptor projects a respective representation of light emitters204 ₁ and 204 ₂ on the optical sensor of moving optical detector 210.Pose processor 214 associates each one of these representations with arespective one optical receptor, according to the position of therepresentation on the optical sensor.

Pose processor 214 associates the representations of light emitters 204₁ and 204 ₂ with the respective optical receptor, projecting theserepresentations on the optical sensor, by tracking the representationson the optical sensor (i.e., after the representation of light emitters204 ₁ and 204 ₂ where associated with a respective optical receptor atleast once). Alternatively, pose processor 214 associates therepresentations of light emitters 204 ₁ and 204 ₂ with the respectiveoptical receptor, projecting these representations on the opticalsensor, by determining a figure of merit for each representation (e.g.,according to the orientation resulting from each representation). Poseprocessor 214 selects the optical receptor with the higher figure ofmerit. In yet another alternative, when light emitters 204 ₁ and 204 ₂are in the FOV of all the optical receptors of moving optical detector210, pose processor 214 associates the representations of light emitters204 ₁ and 204 ₂ with the respective optical receptors according to thegeometric configuration of the optical receptors.

Reference is now made to FIGS. 5A, 5B, 5C and 5D which are schematicillustrations of images of a single light emitter acquired by a WFOVoptical detector which includes only two adjacent optical receptors (notshown). In FIGS. 5A, 5B, 5C and 5D the WFOV optical detector moves fromleft to right relative to the light emitter. Consequently, emitterrepresentation 232 and 236 of the light emitter (not shown), in images230, 234, 238 and 240, move from right to left (i.e., relative to theimage vertical axis), as designated by the arrow. In image 230 (FIG.5A), emitter representation 232 represents the light received from thelight emitter and received by the first optical receptor. In images 234and 238 (FIGS. 5B and 5C), emitter representations 232 and 236 representthe light received from the light emitter and received by both theoptical receptors. In image 240 (FIG. 5D), emitter representation 236represents the light received from the light emitter and received by thesecond optical receptor. Thus, by tracking the representations of thelight emitter, a pose processor (e.g., pose processor 214 in FIG. 4)determines which optical receptor in the WFOV optical detector projectsthe light received from a light emitter. During initialization of thesystem or when the optical tracking system loses track of the movingobject, the optical tracking system has no information relating to whichone of the optical receptors projects light on the optical sensor.Therefore, the system computes a figure of merit for the orientationresulting by considering each representation and selects the opticalreceptor with the higher figure of merit.

According to another embodiment of the disclosed technique, the spatialsetup of the light emitters and the detectors enables the opticaltracking system to determine the orientation of a moving object, in areference coordinate system, without determining the position of theobject. According to this spatial setup, a light emitter is placed atthe entrance pupil of each optical receptor and emits light therefrom.Alternatively, a virtual representation of the light emitter can becreated at the entrance pupil of the optical receptor (e.g., using beamsplitters situated in front of the entrance pupil of the opticalreceptor). Consequently, the light emitter is perceived as emittinglight from the entrance pupil of the optical receptor. In yet anotheralternative, two light emitters are placed such that the optical centerof gravity thereof (e.g., the average position vector, in the referencecoordinate system, of the two light emitters) is located at the entrancepupil of the optical receptor. Referring back to FIG. 4, a virtualrepresentation (not shown) of light emitter 212 is formed at theentrance pupils of the optical receptors of moving optical detector 210.Reference light emitters 204 ₁ and 204 ₂ are positioned such that theoptical center of gravity thereof is located at the entrance pupil ofthe optical receptor of reference optical detector 206. Consequentlyorientation processor determines the orientation of moving object 208without determining the position thereof.

Reference is now made to FIG. 6 which is an example for determining thehorizontal orientation of a moving object without determining theposition thereof in accordance with another embodiment of the disclosedtechnique and still referring back to FIG. 4. It is noted that inexemplary FIG. 6, the position of moving object 208 changes in the X, Yplane of two-dimensional (2D) coordinate system 240, and the orientationof moving object 208 may change only horizontally. It is further notedthat the example brought herein is operative in either one of two cases.In the first case the light emitters emit light from the entrance pupilof the optical receptor of the optical detector. In the second case atleast two light emitters are situated such the optical center of gravitythereof is located at the pupil of the optical detector. It is alsonoted that the roll angle is assumed to be zero.

Pose processor 214 determines the angle α, between the longitudinal axis240 of reference coordinate system 236 and line 238 connecting entrancepupil 232 and entrance pupil 234 of moving optical detector 206 andreference optical detector 210 respectively. Pose processor 214determines this angle α according to the location of a representation ofmoving light emitter 212 in an image acquired by reference opticaldetector 206. For example, when the optical sensor of reference opticaldetector 206 is a CCD sensor, each pixel in the CCD is associated withan angular step. Thus, angle α is that angular step multiplied by thenumber of horizontal pixels counted from the optical center of the CCD.It is noted that moving light emitter 212 emits light from the entrancepupil of the optical receptor of moving optical detector 210 (e.g., viaa beam splitter).

Pose processor 214 determines the angle γ, between the optical axis ofthe moving optical detector 210 and Line 238 connecting entrance pupil232 and entrance pupil 234. Pose processor 214 determines the angle γaccording to the location of the representations of reference lightemitters 204 ₁ and 204 ₂ on an image acquired by moving optical detector210. The optical center of gravity of reference light emitters 204 ₁ and204 ₂ is situated at the entrance pupil of the optical receptor ofreference optical detector 206.

Pose processor 214 determines the horizontal orientation of movingobject 208 by determine the angle between optical axis of the movingoptical detector 210 and longitudinal axis 240, designated by the angleβ. Orientation processor determines the angle β according to:β=γ−α  (1)Thus, according to the example brought hereinabove, orientationprocessor 214 determines the horizontal orientation angle of movingobject 208 without determining the position thereof.

As mentioned above, the exemplary method described in conjunction withFIG. 6 is operative when the light emitters emit light from the entrancepupil of the optical receptor and the roll angle is zero. The method mayalso be operative when the roll angle is substantially small, resultingin an approximation of the azimuth and elevation angles. Alternatively,the method described in conjunction with FIG. 6 is operative insituations wherein the roll angle is known. For example, the two lightemitters are situated such that the optical center of gravity thereof islocated at that entrance pupil (i.e., the roll angle is known accordingto the representations of the two light emitters on the opposite opticalsensor). In yet another example, the roll angle is known fromgravitational tilt sensors. For the exemplary method of FIG. 6 to beoperative with the WFOV optical detector described in conjunction withFIGS. 2A, 2B, 3A and 3B, a light emitter is associated with a respectiveone entrance pupil described therein, and emits light therefrom.Alternatively, at least a pair of light emitters is associated with arespective one entrance pupil and the optical center of gravity thereofis located at that respective entrance pupil. Furthermore, when light isdetermined as entering through an entrance pupil or pupils, associatedwith the light emitter or light emitters, the optical tracking systemrelates to the light emitted by this light emitter or these lightemitters (e.g., by selecting the representation of the light emitter oremitters on the opposite optical detector or by enabling these lightemitters).

The method described in conjunction with FIG. 6 may be applied whenmoving object 208 moves in three-dimensions (3D). Accordingly, theorientation of moving object 208 may change in the horizontal, verticaland roll directions. Equation (1) may be applied in both the horizontaland vertical cases. The results of equation (1) are a horizontalorientation angle and a vertical orientation angle. The azimuth andelevation are approximated according to the horizontal orientation,vertical orientation and roll angles. The roll angle may be determined,for example, as mentioned above, according to the representations of thetwo light emitters on the opposite optical sensor.

According to a further embodiment of the disclosed technique, areflective surface replaces the reference detector. Thus, the opticaltracking system determines the orientation of a moving object, in areference coordinate system, without determining the position of themoving object. According to this configuration, the optical trackingsystem includes a light emitter attached to the moving object and areflective surface situated at a known position in the referencecoordinate system. A reflection of the moving light emitter is formed onthe fixed reflective surface. When the roll angle is substantiallysmall, the reflection of the moving light emitter is affected only bythe change in the azimuth and the elevation angles of the moving object(i.e., yaw and pitch), and not by the translation of the moving object(i.e., there is no parallax). Consequently, the optical tracking systemdetermines the two angle orientation of the moving object according toan image of the reflection of the moving light emitter, acquired bymoving light detector. For determining the roll angle (i.e., whenaccurate values of the azimuth and elevation angles are required), thereflective surface may include additional emitters at the vicinitythereof.

Reference is now made to FIG. 7, which is a schematic illustration of anoptical tracking system, generally reference 250, constructed andoperative in accordance with a further embodiment of the disclosedtechnique. System 250 includes a moving object 252, a reflective surface254 and an orientation processor 256. Moving object 252 includes amoving optical detector 258 and light emitter 260. Moving opticaldetector 258 may be a WFOV optical detector as described hereinabove inconjunction with FIGS. 2A and 2B or FIGS. 3A and 3B. Moving opticaldetector 258 and light emitter 260 are all coupled with orientationprocessor 256. Light emitter 260 emits light toward reflective surface254. Reflective surface 254 reflects the light back toward moving WFOVoptical detector 258. Reflective surface 254 is, for example, a flatmirror. Reflective surface 254 may further be any surface reflecting thelight emitted by Light emitter 260 such as a computer screen, atelevision screen, a vehicle or aircraft windshield and the like.Reflective surface 254 may be a wavelength selective reflective surface(i.e., reflective surface 254 reflects radiation within a range ofwavelengths only). Moving optical detector 258 acquires an image of thereflection of moving light emitter 260. Orientation processor 256determines the orientation of moving object 252 according to theacquired image of the reflection of light emitter 260. Orientationprocessor 256 determines the azimuth and elevation angles of the movingobject according to the (x, y) location of the light emitter in theimage (i.e., when the roll angle is substantially small). However,system 250 described hereinabove in conjunction with FIG. 7, determinesthe azimuth and elevation angles only. When system 250 is required todetermine the roll angle as well, two additional light emitters arefixed, for example, at either side of reflective surface 254. System 250determines the roll angle according to the position of the two lightemitters in the image. Alternatively, a single light emitter of a shapeexhibiting rotational asymmetry around an axis normal to the objectplane (i.e., where the light emitter is located), within a desired rangeof roll angles (e.g., an ellipse, an isosceles triangle) is fixed at thevicinity of the reflective surface.

Reference is now made to FIG. 8, which is a schematic illustration of atwo-dimensional example for determining the orientation of a movingobject without determining the position thereof in accordance withanother embodiment of the disclosed technique and referring back to FIG.6. Orientation processor 256 determines the orientation of moving object252, designated by the angle β, by determining in which angular sectionof the observed scene mirror image 264 of moving light emitter 260 issituated (i.e., by tracking light incident on the sensor of movingoptical detector 258). Orientation processor 256 determines the angle βfurther, according to the location of the projection of mirror image 264of moving light emitter 260 on moving optical detector 258. As in theexample brought hereinabove, when the optical sensor of moving opticaldetector 258 is a CCD sensor, each pixel in the CCD is associated withan angular step. Thus angle β is that angular step multiplied by thenumber of pixels counted from the optical center of the CCD sensor. Asmentioned above, the angle β is determined when the roll angle issubstantially small.

It will be appreciated by persons skilled in the art that the disclosedtechnique is not limited to what has been particularly shown anddescribed hereinabove. Rather the scope of the disclosed technique isdefined only by the claims, which follow.

1. An optical tracking system for determining the pose of a movingobject in a reference coordinate system, the system comprising: at leastone light emitter attached to said moving object; at least one otherlight emitter situated in a fixed position in a reference coordinatesystem; at least one Wide Field Of View (WFOV) first optical detectorattached to said moving object, said WFOV optical detector including anoptical sensor for sensing light received from at least one of said atleast one light emitter, and at least two optical receptors opticallycoupled with said optical sensor, each of said optical receptorsincluding an entrance pupil, said optical receptors being spatiallyspaced apart from each other, each of said optical receptors projectinga different angular section of an observed scene on said optical sensor;a second optical detector situated at said fixed position in saidreference coordinate system; and a pose processor coupled with saidfirst optical detector, with said second optical detector, with said atleast one light emitter attached to said moving object, and with said atleast one light emitter situated at said fixed position, for associatingat least one representation of one of said at least one two lightemitters situated at a fixed position on an image acquired by saidoptical sensor, with a respective one optical receptors projecting thelight received from said one of said at least one two light emitterssituated at a fixed position, on said optical sensor, according to theposition of said representation on said image.
 2. The WFOV opticaldetector according to claim 1, wherein the optical axes of said at leasttwo optical receptors are unparallel with respect to each other.
 3. TheWFOV optical detector according to claim 1, wherein each of said atleast two optical receptors has a different focal length, and whereineach of said at least two optical receptors is one of an optical lensand a pinhole receptor.
 4. The system according to claim 1, wherein saidsecond optical detector is a WFOV optical detector including: an opticalsensor, for sensing light received from said at least one light emitter;and at least two optical receptors, optically coupled with said opticalsensor, each of said optical receptors including an entrance pupil, saidoptical receptors being spatially space apart from each other, each ofsaid optical receptors projecting a different angular section of anobserved scene on said optical sensor.
 5. The system according to claim1, wherein at least two light emitters are attached to said movingobject.
 6. The system according to claim 1, wherein said at least onelight emitter attached to said moving object is of a shape exhibitingrotational asymmetry around an axis normal to the object plane of saidlight emitter, within a desired range of angles.
 7. The system accordingto claim 1, wherein said at least two light emitters are situated in afixed position in the reference coordinate system.
 8. The systemaccording to claim 1, wherein said at least one light emitter situatedin a fixed position is of a shape exhibiting rotational asymmetry aroundan axis normal to the object plane of said light emitter, within adesired range of angles.
 9. The system according to claim 1, whereinsaid pose processor associates said at least one representation with arespective one optical receptor by tracking said representations. 10.The system according to claim 1, said pose processor associates said atleast one representation with a respective one optical receptor bydetermining a figure of merit for each one of said at least onerepresentation and selecting the representation with the higher figureof merit.
 11. The system according to claim 1, wherein said poseprocessor associates each one of said representations, with acorresponding optical receptor, according to the geometric configurationof said at least two optical receptors.
 12. The system according toclaim 1, wherein said optical sensor is selected from the groupconsisting of: a charge coupled device; a complementary metal oxidesemiconductor sensor; a position sensitive device; and a lateralphoto-detector.
 13. The system according to claim 1, wherein saidorientation processor determines an orientation angle of said movingobject by subtracting a first angle from a second angle therebydetermining said orientation angle of said moving object in saidreference coordinate system.
 14. The system according to claim 13,wherein said orientation angle is the horizontal orientation angle, andwherein an azimuth orientation angle is approximated according to saidhorizontal orientation angle.
 15. The system according to claim 13,wherein said orientation angle is a vertical orientation angle, andwherein an elevation orientation angle is approximated according to saidvertical orientation angle.
 16. The system according to claim 13,wherein said first angle is determined according to the directionalresponse of said optical detector situated at a fixed position, to anacquired image of said at least one light emitter attached to saidmoving object, and wherein said second angle is determined according tothe directional response of said optical detector attached to saidmoving object to an acquired image of said at least one light emittersituated at a fixed position.
 17. The system according to claim 7,wherein the optical center of gravity of said at least two lightemitters situated at a fixed position is located at the entrance pupilof said second optical detector situated at a fixed position, andwherein said pose processor determines the roll angle according to theposition of the representations of said at least two light emitterssituated at a fixed position on an image acquired by said opticaldetector attached to said moving object.
 18. The system according toclaim 5, wherein the optical center of gravity of said at least twolight emitters attached to said moving object is located at the entrancepupil of said WFOV first optical detector attached to said movingobject, and wherein said pose processor determines the roll angleaccording to the position of the representations said at least two lightemitters attached to said moving object on an image acquired by saidsecond optical detector situated at a fixed position.
 19. The systemaccording to claim 1, wherein said at least one light emitter attachedto said moving object and at least two reference light emitters situatedin a fixed position are Light Emitting Diodes.
 20. The system accordingto claim 1, wherein a reflective surface is situated at a fixed positionin said reference coordinate system instead of said at least one lightemitter and said at least one optical detector situated at a fixedposition in said referenced coordinate system, wherein said opticaldetector, attached to said moving object, detects light reflected fromsaid reflective surface, and wherein said pose processor determines theorientation of said moving object in said reference coordinate systemaccording to the light incident on said optical detector.
 21. The systemaccording to claim 20, wherein two additional light emitters are fixedin the vicinity of said reflective surface.
 22. The system according toclaim 20, wherein another light emitter is fixed in the vicinity of saidreflective surface and wherein said another light emitter is of a shapeexhibiting no rotational symmetry around an axis normal to the objectplane of said light emitter, within a desired range of angles.
 23. Thesystem according to claim 20, wherein said reflective surface is awavelength selective reflective surface, and wherein, said reflectivesurface is selected from the group consisting of: a mirror; a computerscreen; a television screen; a vehicle windshield; and an aircraftwindshield.
 24. The system according to claim 1, wherein said referencecoordinate system moves with respect to another coordinate system.